Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
2000-12-11
2003-10-28
Fuller, Rodney (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S053000
Reexamination Certificate
active
06639650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pellicle for lithography, that is, a pellicle for lithography used as a dust guard in the production of semiconductor devices such as LSI and VLSI or liquid crystal display panels, in particular, a pellicle for lithography used for laser beam light exposure used in light exposure which requires high resolution. Furthermore, the present invention relates to a light exposure method and light exposure apparatus for lithography utilizing a pellicle as well as a method for relieving warpage of a pellicle membrane.
2. Related Art
In the production of semiconductor devices such as LSI and VLSI or liquid crystal display panels, patterning step is conventionally performed by irradiating light on original substrates for semiconductor devices (semiconductor wafers) or original substrates for liquid crystal panels. In this case, dust particles adhered to a light exposure original (photomask) to be used may cause problems. That is, a transferred pattern may be deformed or edge lines of the pattern may be rugged without smoothness, because the dust particles may absorb or reflect the light. Therefore, dimension, appearance, quality and so forth of the pattern may be degraded, and thus performance and production yield of semiconductor devices, liquid crystal display panels and the like may be degraded.
For this reason, these operations are usually performed in a clean room. However, because it is difficult to keep a light exposure original always clean even in such a clean room, a pellicle well transmitting light is applied to a surface of the light exposure original for dust particle guard. That is, a pellicle is adhered to a mask (in the present invention, a light exposure original and a support substrate for the light exposure original are collectively referred to as “photomask” or “mask”) in order to prevent adhesion of dust particles on the light exposure original used for the light irradiation.
In this case, if a pellicle is applied to a mask, dust particles do not adhere directly on the light exposure original, but on the pellicle membrane. Therefore, if the light is focused on the pattern of the light exposure original during the lithography process, the dust particles on the pellicle are defocused, and hence it provides an advantage that the presence of such dust particles does not influence on the pattern transfer.
As shown in
FIG. 1
, such a pellicle generally comprises a thin pellicle membrane
1
, frame
3
, membrane adhesive
2
that adheres the pellicle membrane
1
to the frame
3
and reticle adhesive
4
that adheres the pellicle
11
to a mask
5
.
Such a pellicle
11
as shown in
FIG. 1
has a structure that a transparent pellicle membrane
1
made of a material well transmitting light such as nitrocellulose, cellulose acetate and fluoropolymer is adhered to one surface of a pellicle frame made of aluminum, stainless steel, polyethylene or the like. In the structure, the pellicle is adhered to the pellicle frame by applying a solvent well dissolving the pellicle membrane
1
on one side surface of the pellicle frame
3
and dried in air (refer to Japanese Patent Laid-open Publication No. 58-219023), or with a membrane adhesive
2
such as acrylic resin, epoxy resin or fluoropolymer (refer to U.S. Pat. No. 4,861,402, Japanese Patent Publication No. 63-27707 and Japanese Patent Laid-open Publication No. 7-168345). Further, the pellicle has an adhesive layer (reticle adhesive)
4
comprising a polybutene resin, polyvinyl acetate resin, acrylate resin, silicone resin or the like and a release layer (separator, not shown) that protects the adhesive layer, which are adhered on the other side. As the pellicle membrane
1
, a pellicle thick plate
7
(
FIG. 5
) such as a glass thick plate may be used. At the time of lithography, the pellicle
11
is adhered beforehand to a mask
5
, before it is mounted on a light exposure apparatus. This adhesion to the mask
5
is attained by peeling the release layer and pressing the pellicle
11
to the mask
5
by applying a load. Therefore, the adhesive layer
4
of the pellicle
11
must have a certain thickness and elasticity.
The mask
5
adhered with the pellicle
11
is held and transferred by a mask holding part
8
(
FIG. 2
) of a light exposure apparatus, and then exposed to light at a predetermined position on the light exposure apparatus.
As for the adhesion of a conventional pellicle
11
and mask
5
, there may be a case where a surface of pellicle membrane
1
(henceforth referred to as “pellicle membrane surface”) is not parallel to a surface of a light exposure original of mask
5
(henceforth referred to as “mask surface”).
As the cause of the above phenomenon, there can be mentioned uneven thickness of the adhesive layer provided on the lower surface of the frame
3
, uneven pressing upon adhesion, dimensional error in processing of the frame
3
itself and so forth.
If the pellicle membrane surface and the mask surface are not parallel, light passing through the pellicle is distorted and such distortion is transferred on the light-exposed original to be irradiated with the light. Therefore, distortion of circuit pattern is caused on the light-exposed original. This distortion causes a deviation of the pattern line width of the circuit pattern on the light-exposed original, and leads to decrease of yield. Under the recent situation that a wavelength of the light to be used becomes shorter and is shifted to ultraviolet light due to use of finer mask pattern, it becomes increasingly important to secure the parallelism of the pellicle membrane surface and the mask surface.
Further, when a thick plate composed of glass or the like is used as a pellicle thick membrane
7
, since it is a thick plate, the interference effect by a thin membrane is eliminated and the reflection at the surface of the pellicle thick plate becomes strong. Moreover, since the pellicle thick plate optically serves as a lens, it becomes more important to secure parallelism of the pellicle membrane surface and the mask surface.
However, in conventional light exposure apparatuses, no attention has been paid at all for adjustment of the parallelism between the pellicle membrane surface and the mask surface.
Moreover, as described above, the resolution of lithography has gradually become higher in recent years, and to realize such resolution, light of a shorter wavelength has gradually come to be used as a light source. Specifically, ultraviolet lights (g-line with wavelength of 436 nm and i-line with wavelength of 365 nm) are currently replaced with far-ultraviolet lights (KrF excimer laser, wavelength of 248 nm), and vacuum ultraviolet lights (ArF excimer laser, wavelength of 193 nm) are ready to be put into practical use in near future. Furthermore, in the lithography using F
2
(fluorine) excimer laser (158 nm) in order to realize higher resolution, use of glass plates composed of an inorganic compound or the like as the pellicle membrane is examined.
As the inorganic compound that can be used as the pellicle membrane, substances showing high transmittance in the vacuum ultraviolet region can be used. Specifically, fluorine-doped quartz glass, magnesium fluoride, calcium fluoride, lithium fluoride, aluminum oxide and so forth can be mentioned, and vitreous transparent plates of these are used.
When these inorganic compounds are used as the pellicle membrane, the membrane is desired to have a thickness of 0.1 mm or more in view of strength. However, in such a case, there may be caused a phenomenon that the inorganic compound plate (hereafter it may be referred to as “glass plate”) may be deflected by its own weight. This deflection may cause deviation of light path for light exposure at the pellicle membrane surface, and thus adversely affect the light exposure.
SUMMARY OF THE INVENTION
The present invention was accomplished in order to solve these problems, and its object is to improve resolution in the lithography using a pellicle. That is, one of the specific obj
Esplin D. Ben
Fuller Rodney
Shin-Etsu Chemical Co. , Ltd.
LandOfFree
Light exposure method, light exposure apparatus, pellicle... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light exposure method, light exposure apparatus, pellicle..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light exposure method, light exposure apparatus, pellicle... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3116767